1. Field of the Invention
The present invention relates to a photonic crystal and a producing method thereof, and more particularly to a photonic crystal capable of efficiently introducing external light and producible with a high yield, and a producing method thereof. The term “light” herein is a concept including, not only visible light, but also electromagnetic waves of longer or shorter wavelengths than the visible light.
2. Description of the Background Art
In recent years, a photonic crystal of a multi-layered structure formed of at least two kinds of dielectric, semiconductor or other materials, having a periodic structure with the refractive index distributed periodically, has attracted an attention. In the photonic crystal, if the refractive indices of the materials and the periodic structure are set appropriately, a frequency band forbidding light propagation appears, which is called a photonic bandgap. The photonic bandgap can suppress propagation of the light having a particular frequency within the photonic crystal. Further, introduction of a defect in the periodic structure of the photonic crystal creates a certain frequency band permitting light propagation within the photonic bandgap, so that the light within the photonic crystal can be deflected or diverged freely. Taking advantage of these characteristics, the photonic crystal can be adapted to an optical resonator or an optical waveguide. In the future, a micro-optical circuit or an optical demultiplexer may be implemented with the photonic crystal.
Methods applicable in production of such a photonic crystal are disclosed, e.g., in Japanese Patent Laying-Open Nos. 2000-150340 and 2000-162459.
The method disclosed in Japanese Patent Laying-Open No. 2000-150340 relates to an exposure method wherein an optical aligner is used for photolithography to expose a lattice pattern on a photoresist. In this method, at least two kinds of patterns are multi-exposed for patterning. With this method, contrast in light intensity between the exposed portion and the non-exposed portion can be increased, which ensures formation of a fine lattice pattern.
In the method disclosed in Japanese Patent Laying-Open No. 2000-162459, firstly, a semiconductor layer is formed on a single crystal substrate. Thereafter, an atomic force microscope fine working method or the like is used to periodically oxidize the surface of the semiconductor layer to thereby form a fine oxide mask. A prescribed thin film material layer is formed on the semiconductor layer in the portion where the oxide mask is not formed, while it is not formed in the portion where the oxide mask is formed. With this method, a high-quality photonic crystal free from sub-micron order damages can be produced.
The conventional photonic crystals produced by the above-described methods and others, however, would pose a problem that external light is not introduced therein efficiently. An optical circuit component made of the photonic crystal that cannot guarantee efficient introduction of external light may become defective. As such, there has been a demand for production of a photonic crystal capable of efficiently introducing external light with a high yield, so as to improve the manufacturing yield of the optical circuit components made of the photonic crystals.